Synthetic fibers having novel shape

ABSTRACT

SYNTHETIC, MOLECULARLY ORIENTED FIBERS OF FINE PITCH AND HAVING LARGE CONCAVITIES AND CONVEXITIES COMPRISING A MELT-SPINNABLE SYNTHETIC POLYMER HAVING A SINGLE CONTINUOUS MALE SCREW SHAPE WHEREIN THE RATIO OF PITCH TO OUTER   DIAMETER OF THE SCREW THREAD IS WITHIN THE RANGE OF 0.3 TO 15, AND THE RATIO OF HEIGHT TO OUTER DIAMETER OF SAID THREAD IS IN THE RANGE OF FROM 0.03 TO 0.4.

March 2 1971 TERUMICHI ONO ETAL SYNTHETIC FIBERS HAVING NOVEL SHAPEFiled Aug. 4, 1966 United States Patent US. Cl. 161-179 6 ClaimsABSTRACT OF THE DISCLOSURE Synthetic, molecularly oriented fibers offine pitch and having large concavities and convexities comprising amelt-spinnable synthetic polymer having a single continuous male screwshape wherein the ratio of pitch to outer diameter of the screw threadis within the range of 0.3 to

15, and the ratio of height to outer diameter of said thread is in therange of from 0.03 to 0.4.

This invention concerns novel synthetic fibers having a unique form, andparticularly concerns synthetic fibers having a male scre-W shapestructure of a specific dimension.

Synthetic fibers have excellent physical properties and durability whichare not seen in natural fibers, and because of these properties, theyhave found wide applications in clothing and as industrial fibers.However, synthetic fibers obtained by melt-spinning method have a gravedrawback in that they have a smooth surface and a strong waxy feeling.

It has been known to improve the feeling and luster of fibers by makingthe cross sections of fibers into those of different shapes such as fiator triangular shape or changing the thickness of fibers along theselengths in the manufacture of synthetic fibers. However, none of theprior art methods of spinning has been able to produce fibers havingmale screw shape in an extruded state.

An object of this invention is to provide novel synthetic fibers whichhave a shape of male screw and because of this, have novel propertieswhich cannot be attained by the conventional fibers.

A specific object of this invention is to provide synthetic fibers whichhave no waxy feeling and a surface having varying states of largeconcavities and convexities at close pitches, which have largeresistance to the deformation of the structures when woven or knitted,and which exhibit a complicated appearance with brilliant portions anddelustred portions intermingled with each other.

Another specific object is to provide monofilamentary synthetic fiberswhich are excellent in knot properties, have a large surface friction,and which are used conveniently as brushes and fishing nets.

Still another object of this invention is to provide a method ofcontinuously producing synthetic fibers of male screw shape having theaforesaid properties without using any particular apparatus.

Other objects and advantages of this invention will become apparent fromthe following descriptions.

The aforesaid objects can be achieved by synthetic fibers comprising amelt-spinnable synthetic polymer which has a structure of a male screwwherein the ratio (p/d) of the pitch (p) to the outer diameter of thethread (d) being in the range of from 0.3 to 15, and the ratio (h/ d ofthe height of the thread (h) to the outer diameter (d) being in therange of from 0.03 to 0.4.

This invention can be widely applied to melt-spinnable syntheticpolymers, but can especially preferably be applied to linear polyamides.The linear polyamide suited 3,567,569 Patented Mar. 2, 1971 for thisinvention includes polycaprolactam (nylon-6), polyhexamethyleneadipamide (nylon-6,6), polyhexamethylene sebacamide (nylon-6,10),poly-w-aminoheptanoic acid (nylon-7), poly-w-aminononanoic acid(nylon-9), polyundecanamide (nylon-ll), polylauriclactam (nylon- 12),polyamide prepared from paraxylene diamine and dodecandionic acid,copolymerised polyamides composed of two or more of these polyamidecomponents, modified polyamides graft or block copolymerized with othermonomers within a range wherein the properties of a linear polyamide arenot substantially changed, a mixture of at least two of the saidpolyamides, and a mixture of the said polyamide with other polyamidescapable of being melted. Among these various linear polyamides,polycaprolactam and polyhexamethylene adipamide are especially suitedfor this invention.

It is of course possible to incorporate into such polymers an ordinarilyused additive such as stabilizers for heat and light, delustrants andpigments.

In order to facilitate the understanding of this invention, reference isto be had to the accompanying drawings in which:

FIG. 1 is an enlarged side view of the synthetic filaments of thisinvention having a male screw structure;

FIG. 2 is illustrative of various dimensions of the synthetic filamentsof this invention having a male screw structure;

FIG. 3 is a diagrammatical view showing the range of conditions for theextrusion of a nylon-6,6 melt in accordance with the method of thisinvention; and,

FIG. 4 is a diagrammatical view showing the range of conditions for theextrusion of a nylon-6 melt in accordance with the method of thisinvention.

As shown in FIG. 1, the synthetic filaments of this invention have amale screw structure having regular pitches in the direction of thefilaments. In FIG. 2, (d) represents the outer diameter of a screwthread; (p), the distance between the screw threads, i.e., pitches; and(h), the height of the thread.

It is essential in this invention that the ratio of the pitch (p) to theouter diameter of the thread (d) should be in the range of from 0.3 to15 The ratios outside the specified range lead to disadvantages. If thisratio is smaller than 0.3, it is impossible for the filaments to engageclosely with each other, and desired effects of this invention cannot beexpected. If, on the other hand, this ratio (p/d) is larger than 15, theengagement of fibers with each other become loosened, and the diffusedreflection and feeling become deteriorated. It is preferable in thisinvention that the said p/ d ratio should be in the range of 0.5 to 10.

Likewise, the height of screw thread should be in an appropriate rangein order to obtain serviceable fibers which have excellent luster andfeeling, and are well engaged with each other. If the height (h) of thethread of the fibers is too small for the outer diameter (d) of thethread, the engagement between fibers is not sufiicient, and the fibersdo not exhibit excellent luster and feeling. The lower limit of a ratioof the height of the thread to the outer diameter of the thread (h/d) is0.03. On the other hand, if the height of the thread is large ascompared with its outer diameter, the properties intended by theinvention are prominently exhibited. But if it is too large, theresistance of the fibers against outer force is lowered and the fibersbecome unserviceable. The upper limit of a ratio of the height to outerdiameter of the thread is 0.4. It is preferable for the purposes of thisinvention that the said h/d ratio should be in the range of 0.05 to0.35.

Suitable synthetic fibers of this invention are drawn in thelongitudinal direction of fibers and molecularly oriented. However, whenthe denier of the said fibers is large, for instance, when the fibersare monofilaments having more than 100 denier, the said fibers have asufficient strength even in an undrawn state, and can be used as such.

In accordance of the method of this invention, the synthetic fibershaving the said male screw shape can be provided by the steps of meltingmelt-spinnable synthetic polymer, extruding it under extrudingconditions with a shear stress capable of producing a melt fracture,thereafter quenching the extruded filamentary melt to set the male screwform of the said melt, and if desired, drawing the extruded filaments intheir longitudinal direction.

The melt fracture is known as a phenomenon in which the outer shape ofan extrudate becomes irregular when a ditficultly fusible polymer or apolymer with a very high melt viscosity is extruded through a capillary.However, in the past, when a polymer having a fiber-forming ability wassubjected to melt-spinning, there was always employed such a conditionthat shear stress to be exerted onto a melt at the time of extrusion islowered as much as possible and the flow of a molten polymer becomessmooth.

Unexpectedly, however, we have found that when a remarkably wellmelt-spinnable synthetic polymer such as a linear polyamide is extrudedunder a specific extruding condition, especially under very high shearstress, there occurs a melt fracture and filaments having a male screwshape can be prepared stably, that by quenching the melt extruded undersuch a condition, the male screw shape produced by the melt fracture canbe set; and that the so formed synthetic fibers having a male screwshape while in a spun state, have excellent physical properties and evenwhen in a drawn state, their male screw structure is maintained.

Such a method of this invention is contrary to the teaching of priormelt-spinning which specifies the carrying out of spinning under acondition with a shear stress rendered as small as possible. It is asurprising discovery that under such a severe extruding condition, therecan be extruded stably continuous filaments having regular male screwshape.

The shear stress (nv), as used in the specification and claims, is avalue determined by the method described in E. B. Bagley, J. Appl.Phys., 28, 624 (1957), and is expressed by the following formula'rW=P'R/Z(L+NR) (1) (where P is an extruding pressure, R is the radiusof an orifice, L is the length of the orifice, and n is a tubelengthcompensating coefficient).

In accordance with the method of this invention, the said melt-spinnablesynthetic polymer is melted, and extruded under a shear stress such thatmelt fracture can occur. The value of the shear stress usable variesdepending upon the type and degree of polymerisation of the polymer tobe used, but generally it should preferably be in the order of at leastWe also found that the shear stress to produce the melt fracture has anupper limit according to the type and degree of polymerisation of apolymer, and when it exceeds the limit, there is a tendency that autilisable melt fracture does not come into existence. This upper limitcan easily be determined experimentally with respect to each polymer.

When polyhexamethylene adipamide is used as the synthetic linearpolyamide, it is preferable that a melt of said polyamide should beextruded under a shear stress expressed by the formula (where 'rWrepresents a shear stress (dyne/cm. and '11) is a relative viscositymeasured in a 98% sulphuric acid at C.).

If the value of nr is less than 2.2, it is extremely difiicult to obtainfibers having a male screw structure of the previously s ecifieddimension. Even if they are obt in d,

their physical properties such as tenacity are so poor that they cannotbe used commercially. On the other hand, when the value of 17) exceeds6.0, it is difiicult to carry out melt-spinning specified in thisinvention.

When polycaprolactam is used as the synthetic linear polyamide, it ispreferable to extrude a melt of the said polyamide under the shearstress expressed by the formula (where 1w represents a shear stress(dyne/cm. and 1;) shows a relative viscosity measured in a 98% sulphuricacid at 25 C.).

For the same reasons as mentioned with respect to polyhexamethyleneadipamide, the value of mof polycaprolactam should preferably be in therange of from 2.0 to 9.0.

FIGS. 3 and 4 show regions operable with respect to polyhexamethyleneadipamide and polycaprolactam. In these diagrams, the axis of ordinatesrepresents a shear stress in terms of dyne/cm. and the axis of abscissarepresents a relative viscosity (7 of the synthetic linear polyamide. Inthese diagrams, the regions surrounded by a solid line show regionswithin which the preparation by melt-spinning of synthetic fibers havinga male screw shape can be carried out.

In accordance with this invention, the fracture of a melt comes intoexistence at a frequency in the order as high as 10 to 10 per secondwhen a melt-spinnable polymer is extruded under the said specific shearstress condition. Therefore, the under the shear stress conditioncapable of producing melt fracture as used in this invention can beexpressed the other way round as under an extrusion condition to producethe melt fracture at a frequency in the order as high as 10 to 10 persecond. This capability of producing a melt fracture at such a highorder of frequency in this invention is also quite unexpected from theprior information in the field of plastics.

It has also been found that in the method of this invention, therelative viscosity of a polymer to be used affects the dimension of themale screw structure. Specifically, the higher the relative viscosity ofthe polymer is, the greater the height of the screw thread becomes.

In accordance with the method of this invention, the so extrudedfilamentary melt is quenched and the male screw shape of the said meltis set The filamentary melt having the male screw structure in that formtravels to some distance from the spinning hole, and then is subjectedto draft by the tension of take-up rolls whereby the filaments in amolten state are drawn. It is preferable according to the invention toquench the melt at a position under the spinneret and above the point atwhich the drawing of filaments in a molten state is started, and then toset the male screw structure of the melt.

The position where a melt extrudate is quenched varies depending uponthe amount of a polymer melt extruded, the take-up speed, thetemperature of a melt extrudate, its relative viscosity, and the denierof the intended fibers, but it is advantageous that generally it is adistance within 50 cm. from the spinneret.

The melt can be quenched by a known means used for the quenching of amolten polymer. For example, a filamentary melt having a male screwstructure is contacted with a cooling medium having a large heatcapacity before a substantial drafting occurs, whereby a latent heat ofmelting is deprived of. A suitable cooling medium is a liquid inert tosynthetic filaments, such as water, an aqueous solution of methanol, anaqueous solution of ethanol and an aqueous solution of ethylene glycol.

The filaments whose male screw structure has been so set have excellentphysical properties in a spun state, and especially when they are themonofilaments with more than 100 denier, they can be used withoutsubsequent drawing.

In a preferred embodiment of this invention, the filaments whose malescrew structure has been so set are subjected to a known drawingoperation to make molecularly oriented filaments having especiallyexcellent physical properties. The drawing should preferably be carriedout at a temperature from room temperature to below the melting point ofthe polymer at a draw ratio of from 3 to 4.5 X

Fabrics woven from the so prepared synthetic fibers of this invention donot give a waxy feeling often seen in fabrics woven from conventionalsynthetic fibers, because of small pitches and large convexities andconcavities, and show diffused reflection like that of a pear becausethe surface is varied in its state. The fabrics are also strong inresistance to deformation of the structure as often seen in conventionalfabrics. The synthetic fibers also give knitted goods having a largeresistance to run and large resistance to expansion and contraction.

The monofilaments in accordance with this invention have excellent knotproperties, a large surface resistance,

a unique surface appearance, an excellent dyeability, fiexibility andphysical tenacity, and because of these excellent characteristics, theyare very useful as brush bristles, nets, guts for rackets, ropes, cords,wigs, etc. In addition, the products of this invention are used in theform of batt, felt, paper and other non-woven fabrics either by cuttingthem to certain lengths or without cutting them. The male screwstructure gives a high stability of form to products.

The invention will hereafter be explained by way of examples which, itshould be understood, only serve to explain the invention and in no waylimit the invention.

EXAMPLE 1 Nylon-6 having a relative viscostiy in sulphuric acid of 3.4was extruded under the following conditions. Namely, the spinningtemperature is 280 C.; the diameter of the spinneret hole is 0.2 mm.;the holes are cylindrical with a length of 0.2 mm. and 0.6 mm.; and theamount of polymer extruded is 2, 4, 6, 8, 10, 12, 14, 16 and 18 g./min.,respectively. The extrusion condition with various shear stress isobtained as shown in Table 1. When an extruded polymer is cooled withwater at a position immediately under the spinneret, there is obtainedmale screw shaped extrudate as shown in FIG. 1. To determine the outershape of the obtained filaments, the pitches, the height of the screwthread, and the outer diameter of the male screw were measured. Theresults are shown in Table 1. It is understandable from the table thatwhen nylon-6 having a relative viscosity in sulphuric acid of 3.4 isused, it is necessary and sufiicient to adjust the shear stress (valuemeasured by the Formula 1) to 5 10 to 2 10 (dyne/ cm?) to obtain malescrew shaped fibers.

TABLE 1 Extrusion condition Screw shape of fibers Height of screw Outerdiam- Arnount of extruded Shear stress Pitch thread eter of screwpolymer (g./min.) (dyne/emfl) (mm.) (mm.) thread (mm.)

3. 4X10 O O 3. 8X10- 5. 9X10 2. 5X10 3X10 4. 5X10- 6. 9X10 2. 9X10- 6X105. 1X10- 7. 8 10 3. 6X10 10 1()- 5. 3X10- 9. 3X 10 3. 5X10 12x10-5.4)(10- 1.1)(10 4. X10- 11x10- 5. 6X10- 1. 2X 10 8. 4X10- 8 (10 6.X10 1. 7X 11. 4X10 4X10 6. 8X10- 2. 2X 10 0 0 7. 0X 10- EXAMPLE 2 Nylon6 having a relative viscosity in sulphuric acid of 2.7 was extrudedunder the following conditions. Namely, the spinning temperature is 255C.; the diameter of the spinneret hole is 0.2 mm.; the spinneret hole iscylindrical with a length of 0.2 mm. and 0.6 mm.; the amount of thepolymer extruded is 2, 4, 6, 8, 10, 12 and 14 g./min., respectively. Theextrusion condition with various shear Stresses was obtained as shown inTable 2. The extruded polymer was cooled and solidified with water at aposition immediately under the spinneret to form extruded filaments asshown in FIG. 1. The pitch, height, outer diameter of a male screw weremeasured to determine the outer shape of the filaments obtained. Theresults are shown in Table 2. It is understandable that when nylon-6having a relative viscosity of 2.7 in a sulphuric acid is used, it isnecessary and suflicient to adjust the value of shear stress (valuedetermined by Formula 1) to 8 10 to 2 10 (dyne/cm?) to obtain male screwshaped filaments.

TABLE 2 Extrusion condition Screw shape of fibers Height of screw Outerdiam- Amount of extruded Shear stress Pitch thread eter of screw polymer(g./ mm.) (dyne/cmfi) (mm.) (mm.) thread (111111.)

6. 4X10 0 2. 8X1O- 9. 3X10 2. 8X10- 2 10- 4.1)(10- 1. 2X10 2. 8 l0' 410- 4.4X10" 1. (5X10 3.0)(10- GXIO- 4. 8X10- 1. 9x10 4. 2X10 3X10 5.0X10" 2.1)(10 0 0 5. 2X10- 2. 5x10 0 0 5. 3X10- EXAMPLE 3 Nylon-6,6having a relative viscosity in sulphuric acid of 3.1 was extruded underthe following conditions. Namely, the spinning temperature is 290 C.;the diameter of the spinneret hole is 0.2 mm.; the spinneret hole iscylindrical with a length of 0.4 and 0.8 mm.; and the shear stress isvaried as shown in Table 1 by the change of the extrusion speed. Whenthe extruded polymer was cooled and solidified with water at a positionimmediately under the spinneret, there were obtained filaments. Withrespect to the so obtained filaments, the pitch, height and outerdiameter of the male screw were measured. The results are shown in Table3. It is understood from the table that it is necessary and sufiicientto adjust the shear stress within the range shown in Formula 2 for thepurpose of developing melt fracture advantageously and stably, and thatby quenching the extruded melt at a position immediately under thespinneret, filaments having stable male screw shape are obtained.

EXAMPLE 4 Nylon-6,6 having a relative viscosity in sulphuric acid of 2.8was extruded under the following conditions. Namely, the spinningtemperature is 275 C.; the diameter of the spinneret hole is 0.2 mm.;the spinneret hole is cylindrical with a length of 0.2 and 0.4 mm.; theshear stress is varied with the change of the extrusion speed as shownin Table 4. When the extruded polymer was cooled and solidified withwater at a position immediately under the spinneret, there were obtainedmale screw shaped filaments as shown in FIG. 1. With respect to theobtained filaments, the pitch, height, and the outer diameter of themale screw were measured. The results are shown in Table 4. It isunderstood from the table that it is necessary and sufficient to adjustthe shear stress within the range shown in Formula 2 for the purpose ofdeveloping melt fracture advantageously and stably, and that byquenching the extruded melt at a position immediately under thespinneret, filaments having stable male screw shape are obtained.

Nylon-6,6 having a relative viscosity in sulphuric acid of 2.8 was spununder a variety of conditions as shown in Table 5. The used spinnerethole is 0.25 mm. in diameter and 0.25 mm. in length. The oiling andcooling were carried out at a position one meter below the spinneret.The so obtained synthetic fibers of this invention when woven into gauzefabrics, showed excellent properties as shown in Table 5. The producthad 30 warps per centimeter and 27 weft per centimeter.

TABLE 5 Experiment 1 1 2 3 4 Temperature 0.). 300 300 290 290 Amount ofextrusion (g./min.) 3 5 15 20 Take-up speed (m./min.) 206 300 900 1,050Draw ratio 4. 4. 0 4. 0 4. 0 Denier 37 40 41 47 Outer diameter d (mm.)0.070 0.087 0. 082 0.080 Pitch p (mm. 3.2 1. 1 0.031 0.021 Height h (mm.0. 003 0. 010 0. 005 0. 003 p/d ratio 45. 7 14. 1 0. 38 0. 26 h/d ratio0. 04 0. 21 0. 06 0. 04 Knot slip of woven fabrics. Much Little LittleMuch Luster of woven fabrics. Touch of woven fabrics 1 Control.

1 Luster like that of flat surface. 3 Luster like surface of pear.

4 Strong waxy feeling.

5 Strong linen feeling.

6 Weak waxy feeling.

7 Slightly strong waxy feeling.

Experiments Nos. 2 and 3 refer to the fibers in accordance with theinvention, and it was found that they have little knot-slip of wovenfabrics, have a gloss like that of the surface of a pear, have weak waxyfeeling or have strong linen touch. The experiments Nos. 1 and 4 referto the fibers which fall outside the invention, and these fibers havemuch knot slip in woven fabrics and strong waxy feeling. The fibers ofthe experiment No. 1 have a gloss like that of a flat surface.

EXAMPLE 6 Nylon-6 having a relative viscosity in sulphuric acid of 3.2was extruded under the conditions as shown in Table 6, quenched withwater at a position 30 cm. under the spinneret, and taken up. Theobtained filaments were drawn and used as guts for rackets for use inbadminton. It was found as shown in FIG. 6 that the monofilaments withinthe range of this invention are not subject to the knot-slip of theguts, and had increased friction against shuttlecock, showing excellentproperties.

The used spinneret was round in Experiment A with a diameter of 1.0 mm.and a length of 1.0 mm.; round in Experiment B with a diameter of 2.0mm. and a length of 1.0 mm.; and Y-shaped in Experiment C with a slitwidth of 0.4 mm., a slit length of 1.0 mm., and a length of one wing of2.0 mm.

TABLE 6 Experiment Temperature C.) Amount of extrusion (g./min.)

Take-up speed (m./n1in.) Draw ratio Denier Outer diam Pitch p (mm.).Height h (mm.). p/d ratio h/d ratio Knot slip of guts Friction 1 Alittle. 2 Much. 3 High. 4 Small. 5 Slightly high.

EXAMPLE 7 Nylon-6 having a relative viscosity in sulphuric acid of 3.2was extruded under the following conditions, quenched with water at aposition 30 cm. under the spinneret, and taken up. The obtainedmonofilaments were drawn at a ratio of 40X, and the drawn filaments wereused as fishing nets. It was found as shown in Table 7 that the netswithin the range of this invention (2, 3 and 4) have only a littledeviation and showed excellent properties. The used spinneret had a holediameter of 0.5 mm., and a length of 0.5 mm., and the flow-in portion isround-bottomed With one hole.

TABLE 7 Sample number 1 2 3 4 Conditions for production:

Polymer temperature C.) 290 290 290 290 Amount of extrusion (g./mi 50100 Take-up speed (m./min.) 50 80 100 100 Draw ratio 4.0 4.0 4.0 4.0Filaments propert Denier ,340 2,370 2,360 2, 380

Outer diameter of screw thread (mm.) 50 0. 64 0. G5 0. 63

Pitch (mm.) 0 2. 0 2. 5 0. 2

Height (n1m.) 0 0. 20 0.15 0.03

Frequency oftip ovcr(percent) 61.0 71.0 68.0 65.2

Frequency of knot slip (percent) 30 0 0 0 Control.

Frequency of tip over is expressed by the following formula:

Frequency of tip over: (a/ b) X 100 (wherein a is a tension measured themoment a knot formed by binding filaments A and B is deformed bypulling, and b shows a tenacity at the breakage of the filaments thatoccurs by a continuous pulling).

By the term frequency of knot slip is meant a frequency in percentage ofknot slips occurring in the samples at the time when the tenacity of thefilaments is measured by pulling the meshes of the net.

EXAMPLE 8 Nylon-6,6 having a relative viscosity in sulphuric acid of 3.0was spun under various conditions, quenched with water at a position 30cm. below the spinneret, taken up and drawn to 3.5 times the originallength. The obtained filaments were used as fishing nets. It was foundas shown in Table 8 that the fishing nets within the range of thisinvention exhibit excellent properties. The used spinneret was 0.2 mm.in diameter and 0.2 mm. in length, and the flow-in portion isround-bottomed with 10 holes.

TABLE 8 Sample number 1 2 3 Production condition:

Polymer temperature C.) 280 280 280 Amount of extrusion (g./min.) 50 80Take-up sped (m./min.) 67 108 Draw ratio 3. 5 3. 5 3. 5 Properties offilaments:

Denier 2,100 2,106 2,100

Outer diameter (mm.) 0.08 0. 11 0. O9

Pitch (mnr) 0. 00 0.17 0. 45

Height (mm.) 0. 005 0. 03 0.01

p/d ratio 120 1. 5 5.6

h/d ratio 0. 00 0. 25 0. 10 Net: Frequency of knot slip 5 O 0 What Weclaim is:

1. Synthetic fibers of fine pitch and having large concavities andconvexities comprising a melt-spinnable synthetic polymer having asingle continuous male screw shape wherein the ratio (p/d) of pitch (p)to outer diameter (d) of the screw thread is in the range of from 0.3 to15, and the ratio (h/d) of height (h) to outer diameter (d) of the screwthread is in the range of from 0.03 to 0.4, said fibers being drawn andmolecularly oriented along their longitudinal axis.

2. The fibers of claim 1 wherein the melt-spinnable synthetic polymer isa linear polyamide.

3. The fibers of claim 2 wherein the linear polyamide ispolyhexamethylene adipamide having a relative viscosity, measured in a98% sulphuric acid at 25 C., of of 2.2 to 6.0

4. The fibers of claim 2 wherein the linear polyamide is polycaprolactamhaving a relative viscosity, measured in a 98% sulphuric acid at 25 C.,of 2 to 9.

5. The fibers of claim 1 wherein the said p/d value is in the range offrom 0.5 to 10.

10 6. The fibers of claim 1 wherein the said h/d value is in the rangeof from 0.05 to 0.35.

References Cited 5 UNITED STATES PATENTS 2,190,770 2/ 1940 Carothersl6lPolyamide Digest 2,434,533 1/ 1948 Wurzberger 57140I 2,578,74312/1951 Rosenthal 161179 10 2,743,511 5/1956 Genovese 57140I FOREIGNPATENTS 760,179 10/1956 Great Britain 161173 15 ROBERT F. BURNETT,Primary Examiner R. L. MAY, Assistant Examiner US. Cl. X.R.

